Hi Lukasz, I’m no expert but I think the moisture content of the timber when purchased could have a lot to do with it. Also the temperature and humidity of your workshop.

I’m sure others with more experience on this will contribute  and help soon.

Ken 🙂

Good advise George and Ken. Actually, I would say something further. I usually mill stock straightway and make my joints the same day; usually immediately when I can. That way there is usually a very minimal amount of movement. I leave the jointed parts united together even if they are not glued and this constraining prevents most of the distortion tendencies you are experiencing. It’s a mistake to leave wood with one side exposed to a drier (or wetter) atmosphere and the other unable to release or absorb because in general we have no control over the atmospheric moisture content (AMC). That can change in a matter of minutes depending on many things not the least of which is steaming potatoes in the kitchen, hanging out washing or the wind blowing in from the east. I keep wood in my workshop for many months and every time I find good wood I stand ot instead of stacking it. Standing on end allows for air circulation and therefor wood acclimation. My Penrhyn Castle workshop is perfectly climate controlled because of the conservation of the castle itself so my wood is perfect after a period, but, that said, this can play havoc with newly installed wood. When we have a class and students must leave their wood overnight or even for a few days I encourage them to leave the flat boards face to face and slip it into a plastic bin liner tightly closed and as airless as possible. This really helps. When I mill many components for a class, sometimes a couple of hundred pieces, I keep the parts sized together and use shrink wrap to wrap around every surface. That works the very best because it both constrains and prevents the ingress and egress of moisture from the ends of the wood. That’s important, especially on short sections say for boxes. Always remember, life is just like wood. It comes with knots in it.

Ultra thin work pieces are often cut slightly over-sized and allowed to settle overnight before thinning further by removing roughly equal amounts of material from each side of the board.  This tends to maintain a more balanced tendancy toward movement.  Especially if timber is slab sawn.  This method of stock reduction can often help reduce problems as stress is relieved evenly and moisture loss/take-up is kept as even as possible.

The best means of avoiding problems with warping and cupping involves careful timber selection.  A lighter (Weight) board equals drier and tends to be less prone to problems associated with moisture loss.

Use clear, straight grained quarter-sawn/rift sawn stock as often as possible.  More knots and swirls in grain tends to equal more internal board stress as grain patterns diverge, cross and often change direction (Reversing grain).

Interesting, thanks for the link